1. Field of the Invention
The present invention relates to method and apparatus for detecting a skew occurring between a recording surface of an optical disc and a pickup, and more particularly, to skew detecting method and apparatus for detecting a skew in the tangential direction.
2. Description of Related Art
In order to correctly read recording data from a disk-shaped optical disc on which digital data has been recorded as a pit train, a light beam for reading to be irradiated onto the disc needs to be correctly irradiated onto a pit.
When the optical disc is curved, however, an information reading beam is irradiated with an inclination (skew) onto the disc surface. In this case a wavefront aberration, in which a coma aberration is a main component, increases and a waveform of a read signal will be distorted.
In reproducing apparatuses for reproducing recording information from the optical disc, a tilt sensor for detecting an inclination amount (hereinbelow, called a skew amount) of an irradiation angle of the information reading beam for the disc surface is provided. By performing a filtering process to the read signal on the basis of equalizing characteristics according to the skew amount detected by the tilt sensor, the distorted waveform is compensated.
In the case of manufacturing the reproducing apparatus having the tilt sensor, however, since an attaching angle of the tilt sensor itself has to be precisely adjusted, there is a problem such that an assembly of the reproducing apparatus is difficult.
When a detection sensitivity of the tilt sensor is fluctuated due to an aging change or the like, since the filtering process is performed by the erroneous equalizing characteristics, a problem of deterioration of the reliability in a waveform compensation occurs.